1. Field of the Invention
The present invention relates to a biodegradable plastic container having a moisture permeability and more particularly, to a biodegradable plastic container having a moisture permeability manufactured in the forms of a bottle, a blister pack, a medicated paper pouch and the like, by using a novel polyester resin composition under a specific injection and extrusion-molding conditions, thus being able to keep the contents of the container dry without any addition of desiccants and be disposed of without causing environmental contamination.
2. Description of the Related Art
Biodegradable resins have been welcomed worldwide since their first appearance in the market since they can be disposed of without causing environmental contamination and their uses are on the gradual increase these days.
There have been known various kinds of biodegradable resins so far; however, their applications to commercial products have been much limited because their physical properties, molecular weight and biodegradability are not suitable for good molding and quality products.
The aliphatic polyester, known to have a good biodegradable property (J of Macromol. SCI-Chem., A-23(3), 1986, pp. 393-409), have been used as materials in medical, agricultural, fishing and packaging industries and its fields of applications are on gradual growth. However, the conventional type of aliphatic polyesters had disadvantages that their backbone structures were too soft and heat-labile, it had low crystallinity, low melting point, difficulty in molding due to high melt index, poor tensile strength and tear strength. To make these aliphatic polyesters more applicable, many efforts have been exerted to increase the number average molecular weight of the current aliphatic polyester to have more than 30,000, however, it has not been able to obtain aliphatic polyester having a molecular weight greater than 15,000 in the conventional polycondensation system.
As a way to solve these problems of conventional polyesters, a method of manufacturing aliphatic polyester resin having a number average molecular weight of greater than 30,000 by adjusting factors such as reaction temperature, degree of vacuum and amount of catalysts was disclosed in Korean Unexamined Patent Publication No 95-758; however, said aliphatic polyester resin had a low weight average molecular weight and was also heat-labile thus not considered appropriate in molding or forming.
Korean Unexamined Patent Publication No 95-114171 discloses a method of manufacturing aliphatic polyester with a high molecular weight by incorporating monomers such as a polyhydric (at least tri-) alcohol or a poly (at least tri-) hydric carboxylic acid. The above process provided a way to improve the molding and forming properties of the aliphatic polyester resin by introducing the monomers into the reactor to reduce the reaction time and to diffuse the molecules within the product. However, the application of this type of polyester resin was not easy due to the decrease of physical properties such as tensile strength resulted from the drastic increase in low molecular weight polyesters. Besides, the fact that the polyester resin easily becomes a gel type makes it difficult to control the reaction for preparing the polyester resin. There is still another process for increasing the molecular weight of the aliphatic polyester resin. Unexamined Korean Patent Publication No. 95-25072, which discloses the high molecular weight aliphatic polyester resin produced by an isocyanate as a coupling material reacting to an aliphatic polyester resin having a number average molecular weight of 15,000 to 20,000 which is produced by dehydration or de-glycol reaction of the mixture of main materials of (1) an aliphatic(including cyclic type), and (2) an aliphatic (including cyclic type) dicarboxylic acid(or an acid anhydride thereof), and a little of (3) monomer of polyhydric alcohol or polyhydric carboxylic acid (or an acid anhydride thereof). The aliphatic polyester resin obtained in this way had a number average molecular weight of 20,000 to 70,000. However, the above-mentioned process has a few drawbacks that it requires more reaction time thus resulting in poor productivity, and the isocyanate, a coupling material to increase the molecular weight of polyester resin, is known to be a carcinogen so necessitating an extremely careful handling of the ingredient.
The object of the present invention is to manufacture a plastic container having a good biodegradability by using a biodegradable polyester resin composition with a novel structure and excellent physical properties so that it can be degraded in nature without causing environmental contamination when disposed. Another object of the present invention is to manufacture said plastic container so that it can also have a good permeability to both moisture and carbon dioxide in order to keep the contents of a container dry without the addition of desiccants.
The present invention relates to a plastic container comprising polyester resin having 9,000-90,000 of number average molecular weight, 30,000-600,000 of weight average molecular weight, 40-150xc2x0 C. of melting point, 0.1-50 g/10 min of melting viscosity(190xc2x0 C., 2160 g), which has both a good biodegradability and a moisture permeability.
FIG. 1 shows a bottle in accordance with the invention. The bottle or container is shown as reference numeral 3 and includes neck 2 and cap 1.
The resin composition used in the present invention comprises one or more selected from an aromatic dicarboxlic acid (or an acid anhydride thereof) such as dimethyl terephthalate and terephthalic acid, an aliphatic (including cyclic type) dicarboxylic acid(or an acid anhydride thereof) such as succinic acid and adipic acid, an aliphatic (including cyclic type) glycol such as 1,4-butanediol and ethylene glycol, by means of esterification and polycondensation reactions as disclosed in Unexamined Korean Patent Publication Nos. 98-33837, 98-33834, 99-56991 and 99-58816. Further, the polyester resin composition in the present invention has the moisture permeability of 70-120 measured at 37.8xc2x0 C., 90% RH for 24 hrs.
The polyester resin in the present invention is an aliphatic polyester resin which has superior physical properties to resolve the limitations used to be present in the conventional biodegradable types and also provides an excellent biodegradability and a moisture permeability due to its peculiar molecular structure.
The specific physical properties of the biodegradable polyester resin with a moisture permeability in the present invention can be represented as shown in the following Table 1. Here, the moisture permeability was measured at 37.8xc2x0 C., 90% RH for 24 hrs.
According to the present invention, in the case of extrusion molding for the above resins it is preferred to produce flexible materials such as films used for blister packs, wherein the appropriate melting point of the resin ranges from 40 to 100xc2x0 C., more preferably from 70 to 100xc2x0 C. If the melting point is below the above range the forming becomes hard to adjust properly due to slow crystallinity while the quality of the product becomes devalued if it exceeds the range.
Injection molding is generally used in producing hard and durable products and its appropriate melting temperature ranges from 100 to 150xc2x0 C., more preferably from 105 to 120xc2x0 C.; however, if the temperature is too low the quality of plastic container becomes poor. The melting points of conventional polypropylene plastic containers fall between 180 and 220xc2x0 C. and thus the properties of those containers are totally different from the one in the present invention. Injection or extrusion molding using the above resins may be performed under general temperature conditions, however, the preferred temperature ranges from 120 to 190xc2x0 C., and more preferably from 130 to 170xc2x0 C. If the molding is performed at a temperature lower than 120xc2x0 C. it is hard to produce a desirable product because the resins within the screw will not be melted completely while physical properties become poor if it is performed at a temperature higher than 190xc2x0 C. The conventional types of resins have different molding temperature range, e.g., 230-275xc2x0 C. for PP resin and 220-250xc2x0 C. for ABS resin. However, if the resins in the present invention are molded under temperatures for conventional resins, the resins will not be appropriate for molding because they will be easily decomposed by heat and their physical properties will become extremely poor. Further, if the resins in the present invention are kept to stay within the screw of injection or extruder for more than 10 min the molding cannot be well proceeded and subsequently the molded product would not be able to carry the proper properties of container if they are molded.
For the production of highly durable containers, the resin may be combined with an additive to fortify strength selected from talc, calcium carbonate, magnesium stearate, calcium sulfate, sugar powder, particular anhydrous silicate, calcium phosphate, and more preferably by adding 1-60 wt. % of talc or calcium carbonate based on the 100% by weight of resin, which then enables to improve the strength of the resins in the present invention comparable to the conventional resins such as polypropylene, polystyrene or ABS resins. Calcium carbonate is inferior to talc in increasing strength, however, it can be served as a fertilizer and prevent the soils from being acidified when it becomes biodegraded and left on the surface of soils after burial. In addition, the combustion rate of calcium carbonate added resin was better than those of resin alone or talc-added resin in the present invention. Examples of strength fortifiers in manufacturing medical equipments in addition to the above mentioned talc and calcium carbonate are magnesium stearate, calcium sulfate, sugar powder, particular anhydrous silicate, and calcium phosphate.
The biodegradable containers produced according to the present invention have a moisture permeability and are thus able to keep contents in said containers to stay in the original condition without quality deterioration even when exposed to a humid environment. Moreover, the container of the present invention enables to get rid of carbon dioxide as well as all the internal moisture out of the container while preventing external moisture from being introduced. Therefore, the containers produced in accordance with the present invention do not need to add any desiccant even when storing pharmaceutical drugs of tablets or capsules, foods and others which need to be kept dry.
The containers in the present invention can be produced in various forms including bottles, packs for capsules, blister packs, medicated paper pouches, tetrahedrons and the like.